This invention relates to interferon inducer, a process for producing the same and pharmaceutical composition containing the same. Interferon is a substance capable of acting upon animal or human cells to inhibit the growth of a virus and is a type of protein liberated from the cell in response to viral infection. The activity of interferon is specific with respect to an animal species and non-specific with respect to a viral species and may vary, with differing conditions for its induction. It is also known that the growth of certain animal tumour-type viruses may significantly be inhibited by interferon under certain conditions. A substance capable of acting upon animal or human cells to induce interferon is designated as an interferon inducer (hereinafter referred to as IF inducer). Thus an IF inducer is of potential interest in the prevention and treatment of various human and animal diseases caused by viral infection. However, various known IF inducers have never been used in practice for such a purpose because of certain serious defects. Thus is has been believed that IF inducers isolated from microorganisms are in general disadvantageous for therapeutic purpose because of their high toxicity.
Known mitogenic agents isolated from the tissues of higher plants such as phytohemagglitinin, pokeweed mitogen and concanavallin A have IF inducing activity. However, they have never been used for preventing and treating various diseases caused by viral infection with successful result because their IF inducing activity is extremely low. Other IF inducers isolated from the tissues of higher plants are also known. That is, Kojima et al disclosed an IF inducer isolated from the root of Angellica acutiloba Kitagawa (known in Japan as Toki) [Japanese Patent application as laid open to public inspection as Kokai Koho No. 32107/78] and Kojima and Tamamura disclosed an IF inducer isolated from the peeling of a mulbaeery such as Morus alba Linne or Morus bombycis Koidzmi [Japanese Patent application as laid open to public inspection as Kokai Koho No. 99313/78].
Subsequently, we provided an IF inducer having a high IF inducing activity and extremely low toxicity (hereinafter referred to as inducer A) originating from a plant of the genus Carthamus of the family Compositae or a variant thereof containing the inducer A, which may be prepared by extracting the tissue of such a plant with water at a temperature from ambient to the boiling point of the extraction mixture for a period sufficient to extract a major portion of the inducer A present in the tissue, forming a supernatant from the extracted solution to yield fractions containing a major portion of the inducer A present in the supernatant and recovering the inducer A therefrom. Preferred plants for the preparation of the inducer A are exemplified by Carthamus tinctorius Linne.; C. lanatus L.; C. arborescens L.; C. baeticus Nyman and variants thereof and the use of their flowers is preferred because the inducer A is particularly rich in the flowers. The recovery of the inducer A may preferably be effected by ultrafiltration using a suitable membrane for fractionating substances having a molecular weight of from about 200,000 to about 1,000,000 because the molecular weight of the inducer A is from about 100,000 to about 3,000,000 (mainly from about 200,000 to about 1,000,000). The elemental analysis of the inducer A is H: 6.54.+-.0.3%, C: 41.9.+-.0.3%, N: 2.39.+-.0.3% and P: 0.28.+-.0.03%, which is believed to be a polymer of amino acids and sugars containing phosphoric acid [disclosed in our U.S. Pat. application Ser. No. 119,325 which is hereby cited as reference].
As a result of further studies, it has now been found that another IF inducer (hereinafter referred to as inducer B) is present in the tissues (in particular, achens) of the plants of the genus Carthamus or variants thereof and may be isolated therefrom in a similar manner to that applied to the isolation of the inducer A. The IF inducing activity of the inducer B is at least equal or superior to that of the inducer A and its toxicity is also extremely low.